The theory of labor-time as the direct measure of money was first systematically developed by JOHN GRAY.[56] He makes a National Central Bank ascertain through its branches the labor-time consumed in the production of various commodities. The producer receives an official certificate of value in exchange for his commodity. i. e., he gets a receipt for as much labor-time as his commodity contains,[57] and these bank notes of one week’s labor, one day’s labor, one hour’s labor, etc., serve at the same time as a check for an equivalent in all other commodities stored in the bank warehouses.[58] This is the fundamental principle carefully worked out in detail and based throughout on existing English institutions. Under this system, says Gray, “to sell for money may be rendered, at all times, precisely as easy as it now is to buy with money; ... production would become the uniform and never-failing cause of demand.”[59] The precious metals would lose their “privilege” as against other commodities and “take their proper place in the market beside butter and eggs, and cloth and calico, and then the value of the precious metals will concern us just as little ... as the value of the diamond.”[60] “Shall we retain our fictitious standard of value, gold, and thus keep the productive resources of the country in bondage? or, shall we resort to the natural standard of value, labour, and thereby set our productive resources free?”[61] Labor-time being the intrinsic measure of value, why should there be another external measure side by side with it? Why does exchange value develop into price? Why do all commodities estimate their value in one exclusive commodity, which is thus converted into a special embodiment of exchange value into money? That was the problem which Gray had to solve. Instead of solving it, he imagined that commodities could be related directly to each other as products of social labor. But they can relate to each other only in their capacity of commodities. Commodities are the direct products of isolated independent private labors, which have to be realized as universal social labor through their alienation in the process of private exchange, that is to say, labor based on the production of commodities becomes social labor only through universal alienation of individual labors. But by assuming that the labor-time contained in commodities is _directly social_ labor-time, Gray assumes it to be common labor-time or labor-time of directly associated individuals. Under such conditions a specific commodity like gold or silver could not confront other commodities as the incarnation of universal labor, and exchange value would not be turned into price; but, on the other hand, use-value would not become exchange value, products would not become commodities and thus the very foundation of the capitalistic system of production would be removed. But that is not what Gray has in mind. _Products are to be